1. Field of the Invention
This invention relates generally to automotive vehicles such as a motorcycle and more particularly to a rear wheel suspension device.
2. Prior Art
One conventional motorcycle 10 shown in FIGS. 1 and 2 comprises a rear wheel suspension device 12 mounted on a frame 14. The suspension device 12 comprises a swing arm 16 extending along the length of the frame 14 and supporting a rear wheel 18 at a rear end thereof, and bearing means 20 mounted on the frame 14 and pivotally supporting a front end of the swing arm 16 for allowing a swinging movement thereof. The rear wheel suspension device 12 further comprises a cushioning means 22 which comprises a shock absorber 22a. extending between an upper portion of the frame 14 and the swing arm 16, and a coil spring 22b wound around the shock absorber 22a. The swing arm 12 is disposed rearwardly of an engine 24 including a drive shaft 26 having one end extending exteriorly of a body thereof. A drive sprocket 28 is fixedly mounted on the one end of the drive shaft 26, and an endless transmission member 30 such as a chain and a belt is extended between the drive sprocket 28 and a driven sprocket 32 fixedly mounted on the rear wheel 18. The bearing means 20 comprises a pair of roller bearing members 34a and 34b mounted respectively on a pair of parallel spaced loop portions 14a and 14a of the frame 14 through respective mounting plates 36 and 36 and a mounting shaft 38 which extends through the bearing members 34a and 34b and the mounting plates 36 and 36. The front end of the swing arm 16 is bifurcated to provide a pair of spaced arms 16a and 16a secured to the pair of bearing members 34a and 34b, respectively. As best shown in FIG. 2, the bearing member 34a is disposed rearwardly of the drive sprocket 32 and is disposed in registry therewith in the direction of the length of the frame 14. The endless chain 30 is swung vertically about the drive shaft 26 when the swing arm 16 is swung vertically about the axes of the bearing members 34a and 34b. The drive shaft 26 and the bearing members 34a and 34b are considerably spaced from each other in the direction of the length of the frame 14, so that as the vertical movement of the rear wheel 18 increases, the tension of the endless chain 30 is considerably varied. In addition, in motorcycles, it is desired to mount the engine on the frame rearwardly as much as possible to obtain a good weight distribution of the motorcycle without reducing the length of the swing arm. And, it is also desired to increase the length of the swing arm as much as possible without changing a wheel base so as to make the layout of the suspension device less limited. To achieve these, it is necessary to reduce the spacing between the drive shaft 26 and the bearing members 34a and 34b. With the conventional motorcycle 10, this spacing can not be reduced adequately because of a possible interference of the bearing member 34a with the engine body and the drive sprocket 26.